Search Results (148)

This study investigates the complementary noise control capabilities of two passive jet noise mitigation strategies: a traditional ejector nozzle and a novel application of 3M™ Nextel™ 312 ceramic fabric as a thermal–acoustic liner on the central cone of a micro turbojet nozzle. Three nozzle configurations, baseline, ejector, and Nextel-treated, were evaluated under realistic operating conditions using traditional and advanced acoustic diagnostics applied to data from a five-microphone circular array. The results show that while the ejector provides superior directional suppression and low-frequency redistribution, making it ideal for far-field noise control, it maintains high total energy levels and requires structural modifications. In contrast, the Nextel lining achieves comparable reductions in overall noise, especially in high-frequency ranges, while minimizing structural impact and promoting spatial energy dissipation. Analyses in both the time-frequency and spatial–spectral domains demonstrate that the Nextel configuration not only lowers acoustic energy but also disrupts coherent noise patterns, making it particularly effective for near-field protection in compact propulsion systems. A POD analysis further shows that NEXTEL more evenly distributes energy across mid-order modes, indicating its role in smoothing spatial variations and dampening localized acoustic concentrations. According to these results, ceramic fabric linings offer a lightweight, cost-effective solution for reducing the high noise levels typically associated with drones and UAVs powered by small turbojets. When combined with ejectors, they could enhance acoustic suppression in compact propulsion systems where space and weight are critical. Full article

Integrating ejectors into CO₂ transcritical refrigeration systems to reduce energy consumption has been performed successfully throughout the industry in recent years. The objective of the present work is to investigate the effect of indoor and outdoor operating conditions on the energy efficiency of ejector expansion supermarket refrigeration plants. The analysis uses the measured energy consumptions and loads for two supermarket refrigeration plants operating in two cities in the Republic of Moldova (Chisinau and Balti). A model for the prediction of the plant’s annual energy consumption and the loads of the refrigeration and freezing compressors is developed using experimental results. Although there are theoretical and experimental analyses of the investigated systems in the specialized literature, no studies were found in the specialized literature regarding energy consumption increase due to pressure losses through the pipe route in transcritical CO₂ refrigeration installations with an ejector for supermarkets. The results indicate that refrigeration compressors have a greater increase in energy consumption than freezing compressors with increases in the outdoor temperature. The study shows that the additional drop in evaporating pressure at the compressor rack due to incorrect sizing of the pipe route leads to higher energy consumption compared to what the same plant would consume if the pipe route were correctly sized and executed. For every one-degree increase in temperature loss due to additional pressure drop through the pipeline, the entire plant consumes around 1.5% more energy. Knowledge of these performance data of real systems provides designers and manufacturers with clues to understand the importance of the correct design of the pipe route to obtain maximum energy efficiency. Full article

Two-phase expansion processes have emerged as a promising technology for enhancing energy efficiency in power generation, refrigeration, waste heat recovery systems (for example, partially evaporated organic Rankine cycle, organic flash cycle, and trilateral flash cycle), oil and gas, and other applications. However, despite their potential, widespread adoption is hindered by inherent challenges, particularly energy losses that reduce operational efficiency. This review systematically evaluates the current state of two-phase expansion technologies, focusing on the root causes, impacts, and mitigation strategies for expansion losses. This work used Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA). Using the PRISMA framework, 52 relevant publications were identified from Scopus and Web of Science to conduct the systematic review. A preliminary co-occurrence analysis of keywords was also conducted using VOSviewer version 1.6.20. Three clusters were observed in this co-occurrence analysis. However, the results may not be significant. Therefore, the extended work was done through a comprehensive analysis of experimental and simulation studies from the literature. This study identifies critical loss mechanisms in key components of two-phase expanders, such as the nozzle, diffuser, rotor, working chamber, and vaneless space. Also, losses arising from wetness, such as droplet formation, interfacial friction, and non-equilibrium phase transitions, are examined. These phenomena degrade performance by disrupting flow stability, increasing entropy generation, and causing mechanical erosion. Several losses in the turbine and volumetric expanders operating in two-phase conditions are reported. Ejectors, throttling valves, and flashing flow systems that exhibit similar challenges of losses are also discussed. This review discusses the mitigation and the strategy to minimize the two-phase expansion losses. The geometry of the inlet of the two-phase expanders plays an important role, which also needs improvement to minimize losses. The review highlights recent advancements in addressing these challenges and shows optimization opportunities for further research. Full article

To promote renewable energy utilization and enhance the environmental friendliness of refrigerants, this study presents a novel experimental investigation on a transcritical CO₂ double-evaporator heat pump water heater integrating both air and water sources, designed for high-temperature hot water production. A key innovation of this work lies in the integration of an ejector into the dual-source system, aiming to improve system performance and energy efficiency. This study systematically compares the conventional circulation mode and the proposed ejector-assisted circulation mode in terms of system performance, exergy efficiency, and the economic payback period. Experimental results reveal that the ejector-assisted mode not only achieves a higher water outlet temperature and reduces compressor power consumption but also improves the system’s exergy efficiency by 6.6% under the condition of the maximum outlet water temperature. Although the addition of the ejector increases initial manufacturing and maintenance costs, the payback periods of the two modes remain nearly the same. These findings confirm the feasibility and advantage of incorporating an ejector into a transcritical CO₂ compression/ejection heat pump system with integrated air and water sources, offering a promising solution for efficient and environmentally friendly high-temperature water heating applications. Full article

The two-phase ejector has gained prominence in heat pump systems as a device that effectively mitigates throttling losses through expansion work recovery. This investigation employs three-dimensional computational fluid dynamics (CFD) simulations to analyze the parametric effects of the mixing channel geometry on the entrainment characteristics in an R410A ejector. After validating the model according to the experimental data, the parameter analysis was carried out, and four key geometric parameters were changed within a certain range: the nozzle exit position (NXP = 13–19 mm), the pre-mixing channel convergent angle (CA = 20–60°), the diameter ratio (DDR = 5.0–7.1), and the length-to-diameter ratio (LDR = 8.9–12.4). Multi-variable optimization studies revealed optimal geometric configurations at NXP = 17 mm (about 3.5D_mix), CA = 30°, DR = 6.4, and LDR = 11.1, yielding an optimized mass entrainment ratio enhancement of 23.6% compared to baseline designs. This research provides actionable guidelines for the design of high-efficiency ejector components for heat pump applications. Full article

Decarbonisation in hot climates demands innovative cooling solutions that minimise environmental impact through renewable energy integration and advanced system optimisation. This study investigates the energetic and economic feasibility of a thermo-mechanical vapour compression (TMVC) cooling system that integrates a conventional vapour compression cycle with an ejector and a thermally driven second-stage compressor powered by solar-heated water from evacuated flat-plate collectors. The system is designed to reduce mechanical compressor work and enhance cooling performance in hot climates. A comprehensive 4E (energy, exergy, economic, and environmental) analysis is conducted for a multi-story residential building in Baghdad, Iraq, with a total floor area of approximately 8000 m² and a peak cooling demand of 521.75 kW. Numerical simulations were conducted to evaluate various configurations of solar collector areas, thermal storage tank volumes, and collector mass flow rate, aiming to identify the most energy-efficient combinations. These optimal configurations were then assessed from economic and environmental perspectives. Among them, the system featuring a 600 m² collector area and a 34 m³ storage tank was selected as the optimal case based on its superior electricity savings and energy performance. Specifically, this configuration achieved a 28.28% improvement in the coefficient of performance, a 22.05% reduction in energy consumption, and an average of 15.3 h of daily solar-assisted operation compared to a baseline vapour compression system. These findings highlight the potential of the TMVC system to significantly reduce energy usage and environmental impact, thereby supporting the deployment of sustainable cooling technologies in hot climate regions. Full article

The thermally driven ejector refrigeration system is generally used to recover industrial waste heat to improve the energy efficiency of industrial processes. However, for conventional single-stage ejector refrigeration systems (ERSs), the higher-pressure steam derived from high-temperature waste heat elevates the primary fluid pressure, resulting in significant pressure mismatch with the secondary fluid, which consequently leads to large irreversible losses and substantial degradation in system performance. To address this issue, a novel hybrid ejector refrigeration system (NHERS) is proposed and analyzed under design and off-design conditions using thermodynamics. The results indicate that under design conditions, compared to the conventional single-stage ejector refrigeration system, the proposed hybrid ejector refrigeration system can achieve increases of about 20.6% in the entrainment ratio, around 15.2% in the coefficient of performance (COP), and about 21.4% in exergetic efficiency. Analyzing its performance under off-design conditions to provide technical solutions for the flexible operation of the hybrid ejector refrigeration system proposed in this paper can broaden its application scenarios. Consequently, the proposed NHERS demonstrates remarkable superiority in energy conversion and transfer processes, showing certain application prospects in the field of medium- to high-temperature industrial waste heat recovery. Full article

This investigation attempts to develop a tower solar collector-based system designed for the cogeneration of cooling and desalination. The traditional organic Rankine cycle (ORC) integrated with the ejector refrigeration cycle generates limited power and cooling at a single temperature. Acknowledging their limitations, our present study uses an organic flash cycle (OFC) supported by solar heat combined with the two-phase ejector cycle and the reverse osmosis (RO) desalination unit. Since the OFC turbine is fed with two extra streams of fluid, therefore, it provides greater power to run the compressor of the ejector and pumps of the RO unit, resulting in the production of cooling at two different temperatures (refrigeration and air conditioning) and a higher mass flow rate of fresh water. A mathematical model is employed to assess the impact of coil curvature ratio, Rib height, and direct normal irradiation (DNI) on the temperature of the collector’s oil outlet. ANSYS-FLUENT conducts numerical simulations through computational fluid dynamics (CFD) analysis. The results indicate an ultimate increase in oil outlet temperature of 45% as the DNI increased from 450 to 1000 W/m² at a curvature ratio of 0.095 when employing the 1st Rib. Further, a steady-state energy and exergy analysis is conducted to evaluate the performance of the proposed cogeneration, with different design parameters like DNI, coil curvature ratio, rib height, and OFC turbine inlet pressure. The energetic and exergetic efficiencies of the cogeneration system at DNI of 800 W/m² are obtained as 16.67% and 6.08%, respectively. Exergetic assessment of the overall system shows that 29.57% is the exergy produced as cooling exergy, and the exergy accompanied by freshwater, 68.13%, is the exergy destroyed, and 2.3% is the exergy loss. The solar collector exhibits the maximum exergy destruction, followed by the ejector and RO pumps. Integrating multiple technologies into a system with solar input enhances efficiency, energy sustainability, and environmental benefits. Full article

In this study we perform a computational numerical analysis to examine the flow characteristics of a system composed of a rocket engine, supersonic diffuser, and ejector system. When the nozzle expansion ratio of a rocket engine increases, it is necessary to maintain high-vacuum conditions during ground hot testing, which requires a supersonic diffuser and ejector system. The integrated model, consisting of multiple systems and a single-ejector system model, exhibits a difference in the initial volume to be evacuated. Although some differences are observed during the initial vacuum transition process, both models maintain the same final vacuum pressure (4 kPa). During the initial vacuum process, if the injection pressure of the ejector decreases below the design pressure, vacuum degradation occurs because of momentum deficiency, followed by pressure perturbations as the vacuum process resumes. Once the rocket engine ignites and flow is supplied to the suction region, two flow regions exist around the ejector nozzle exit. As these flows mix and move downstream, flow separation occurs in the expansion region. When the injection pressure of the ejector falls below the design pressure, the flow separation region moves forward, and this shift helps maintain the designed vacuum suction conditions. Full article

The exhaust purge on the anode side is a critical step in the operation of fuel cell systems, and optimizing the exhaust interval time is essential for enhancing stack efficiency and hydrogen utilization. This paper proposed a method to determine the purge strategy of hydrogen supply system based on theoretical and simulation analysis. To investigate the impact of anode purge strategy on the performance of automotive fuel cells, a model of a 100 kW fuel cell stack and a dual-ejector hydrogen supply system was developed in MATLAB/Simulink(R2022b) using principles of fluid dynamics, simulation, and experimental data. This model effectively captures the accumulation and exhaust of hydrogen, nitrogen, and vapor within the anode. Simulations were conducted under seven different exhaust interval times at varying current densities to study the effect of exhaust interval on the performance of the fuel cell. The results indicate that for a 100 kW fuel cell, the exhaust interval time should be controlled within 25 s and should decrease as the current density increases. At low current density, increasing the exhaust interval has a more significant effect on improving hydrogen utilization. At high current density, reducing the exhaust interval helps maintain a stable hydrogen excess ratio and shortens the time required for the output voltage to reach a stable state. Full article

Recent advancements in computational and experimental techniques have deepened the understanding of ejector dynamics. Working maps, which depict the relationship between operating conditions and the performance metrics of entrainment and pressure, are commonly used in defining the ejectors’ performances and designs and enhancing their operational flexibility. This paper investigates the sensitivity of a jet ejector to variations in the inlet temperatures, with a focus on how changes in these temperatures affect its performance and Mach number distribution. Using high resolution CFD (computational fluid dynamics) simulations, this study maps ejector behavior by using the ideal gas approximation, marks Mach number scene responses to those changes, and is aimed at optimizing it to work with refrigeration systems using commercial fluid R1234yf/2,3,3,3-Tetrafluoropropene. The findings provide valuable insight into operational conditions for jet ejectors. The analysis revealed little dependence on the changes in inlet temperatures, therefore expanding the design working conditions by at least +20% of the temperature at each of the inlets. This study also analyzes the small deviations in ejector behavior due to temperature variations at the inlets. It contributes to the development of sustainable refrigeration systems, as it broadens the operational temperature range and enhances practical applications in this field, as this information is difficult to find in commercial databases. Full article

Recent research in the liquefied natural gas (LNG) industry has concentrated on reducing specific power consumption (SPC) during production, which helps to lower operating costs and decrease the carbon footprint. Although reducing the SPC offers benefits, it can complicate the system and increase investment costs. This review investigates the thermodynamic parameters of various natural gas (NG) liquefaction technologies. It examines the cryogenic NG processes, including integrating NG liquid recovery plants, nitrogen rejection cycles, helium recovery units, and LNG facilities. It explores various approaches to improve hybrid NG liquefaction performance, including the application of optimization algorithms, mixed refrigerant units, absorption refrigeration cycles, diffusion–absorption refrigeration systems, auto-cascade absorption refrigeration processes, thermoelectric generator plants, liquid air cold recovery units, ejector refrigeration cycles, and the integration of renewable energy sources and waste heat. The review evaluates the economic aspects of hybrid LNG systems, focusing on specific capital costs, LNG pricing, and capacity. LNG capital cost estimates from academic sources (173.2–1184 USD/TPA) are lower than those in technical reports (486.7–3839 USD/TPA). LNG prices in research studies (0.2–0.45 USD/kg, 2024) are lower than in technical reports (0.3–0.7 USD/kg), based on 2024 data. Also, this review investigates LNG accidents in detail and provides valuable insights into safety protocols, risk management strategies, and the overall resilience of LNG operations in the face of potential hazards. A detailed evaluation of LNG plants built in recent years is provided, focusing on technological advancements, operational efficiency, and safety measures. Moreover, this study investigates LNG ports in the United States, examining their infrastructures, regulatory compliance, and strategic role in the global LNG supply chain. In addition, it outlines LNG’s current status and future outlook, focusing on key industry trends. Finally, it presents a market share analysis that examines LNG distribution by export, import, re-loading, and receiving markets. Full article

The subcooling potential of a novel R717-based waste heat-driven multi-ejector chiller (HEC) integrated with an R744 refrigeration system was evaluated for use in supermarkets. The performance was compared with an R744 refrigeration system coupled to R718- and R600a-based HECs, an R744 system equipped with parallel compression (PC), and a standard R744 booster system (CB) in various warm and hot climatic locations. Integration of the R717-based HEC was found to improve the coefficient of performance by 3.7% at 27 °C to 12.1% at 45 °C compared to the R718, and by 1.6% at 27 °C to 7.6% at 45 °C compared to the R600a-based system. The energy-saving potential of the R717 system (6.2% to 9.4%) was also found to be higher than that of the R718 (0.7% to 2.8%) and R600a systems (2.5% to 6.6%). The use of the existing high-pressure controllers of the CB system was found to impose a relatively lower penalty on the system performance compared to the controllers of the PC system. Although the integration of the R718 system incurred a significantly lower additional investment, the recovery time of the R600a-based HEC (2.3–4.8 years) was found to be the shortest. Full article

The primary aim of this work was to share the results from a Research Project supported by the Italian National Research Council, which led to the development of a versatile jacketed tower bioreactor. Designed to optimize oxygen transfer efficiency and process control, the reactor incorporated a reciprocating air compressor, centrifugal pumps, a draft tube with or without perforated plates, and a series of gas–liquid ejectors. Its flexible design enabled operation in both airlift and ejector-loop modes, making it suitable for a wide range of aerobic fermentation processes. By sharing the detailed engineering design, operational procedures of this pilot-scale bioreactor, as well as its performance data when cultivating yeasts on whey and potato wastewater, a detailed blueprint was given to researchers seeking to advance bioreactor technology, particularly in the context of emerging fields like cultured meat production, pharmaceutical manufacturing, and environmental bioremediation. Full article

This work presents a novel trigeneration system for the simultaneous production of desalinated water, electrical energy, and cooling, addressing the challenges of water scarcity and climate change through an integrated and efficient approach. The proposed system combines an 8-stage Multi Stage Flash Distillation (MSF) process with a 6-effect Multiple Effect Distillation (MED) process, complemented by an expander-generator to optimize steam utilization. Cooling production is achieved through a dual ejectocondensation mechanism, which enhances energy recovery and expands operational flexibility. The system’s performance was analyzed using Aspen Plus simulations, demonstrating technical feasibility across a broad operating range: 28.3 to 0.8 kPa and 68 to 4 °C. In cogeneration mode, the system achieves a Performance Ratio (PR) of 12.06 and a Recovery Ratio (RR) of 54%, producing 67,219.2 L/day of desalinated water and reducing electrical consumption by 12.03%. In trigeneration mode, it achieves a PR of 17.81 and an RR of 80%, with a cooling capacity of 1225 kW, generating 99,273.6 L/day of desalinated water while reducing electrical consumption by 3.69%. These results underscore the system’s capability to significantly enhance the efficiency and capacity of thermal desalination technologies, offering a sustainable and high-performing solution for coastal communities worldwide. Full article